Internal combustion engines create drive torque that is transferred to a drivetrain via a crankshaft. The crankshaft torque and engine block dynamic combustion torque are generally equal in amplitude and opposite in direction. Engines are designed to produce a steady-state (DC) torque. Under certain conditions, a dynamic (AC) torque is generated, and can result in noise and vibration that is noticeable by the vehicle occupants.
Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder engine can be operated using four cylinders to improve fuel economy by reducing pumping losses. This process is generally referred to as displacement on demand or DOD. Operation using all of the engine cylinders is referred to as an activated mode. A deactivated mode refers to operation using less than all of the cylinders of the engine (one or more cylinders not active).
Vehicles are tuned to reduce noise, vibration and harshness (NVH). For example, vibrations are induced in the engine and the remainder of the powertrain as a result of the combustion process. The engine and structures supporting the engine in the vehicle (e.g., engine mounts) are tuned to attenuate this vibration.
In the deactivated mode, there are less cylinders operating. As a result, the vibration frequency is reduced. For example, in an 8-cylinder engine, the vibration frequency resulting from combustion is approximately 80 Hz. When operating in a deactivated mode, only 4-cylinders are firing. As a result, the vibration frequency is cut in half to 40 Hz. The reduced vibration frequency in the deactivated mode can result in an increase in NVH, which may be noticeable by the vehicle operator.